Watercraft fin systems come in many flavors. For example, the most common surfboard fin systems have three fins that include two side fins and a central or rear fin.
The two side fins are angled, and the central fin is aligned with the board centerline. The angle of the side fins aids in turning. However, the three fins create increased resistance to water flow by having different angles. If the three fins are aligned, turning is difficult; turning is also more difficult with a single fixed fin. A common attempt to solve this problem is to provide a fin that turns to align with the water flow.
One attempted solution to this problem is found in U.S. Pat. No. 4,733,496, which describes a double fin system that includes a leading blade fixed to the surfboard. A rear half of the fin system is attached to the fixed blade by two pivot pins. Additionally, this system includes a spring-loaded pin for centering the rear half of the fin system relative to the front half. This provides a limited solution to the problem. Much of the force of a surfboard fin is concentrated along the leading edge of the fin, and the leading edge of the fin does not rotate.
Another attempted solution to this problem is found in U.S. Pat. No. 4,854,904, which describes a rotating keel system. This rotating keel system mounts the fin, or keel, in a circular axle, and has limits on rotation either through set screws or through a pie-shaped cutout, and it also has a restoring force to center the fin. However, the rotating keel system lacks a stabilizing mechanism. In particular, there is no securing, or pre-load, force that must be overcome to move the fin out of the center position. This becomes a critical feature because if the fin turns to one side, it will move the rider's weight in a direction opposite of the rear of the watercraft. This will turn the watercraft, and shift the rider's weight to the other side of center. The turning of the fin, and the rider's weight, therefore oscillate out of phase at a critical velocity, and the watercraft becomes destabilized as a result.
Another attempted solution to this problem is found in U.S. Pat. No. 5,070,804, which describes a rotating fin system. The fin of this rotating system is mounted around an axle, and fin rotation is controlled by two force elements that bear on a second shaft perpendicular to the axle. Oscillations are controlled by having the second shaft move over a set of teeth. While this mechanism may provide some amount of frictional dampening, performance will be quantal in rotation, so that the fin will tend to jump from tooth to tooth. Any frictional dampening provided by this system also decreases with wear of the dampening mechanism. Further, there is no pre-load beyond the frictional control of the rotation. Additionally, the use of fin mounted around a narrow axle increases susceptibility to wear and contamination.
Yet another attempted solution to this problem is found in U.S. Pat. No. 6,053,789, which describes a single fin mechanism in which a fin is mounted to a shaft that runs through upper and lower bearing plates that are bearing coupled. The fin rotation of this system however is not resisted by force. Although this system describes a pivoting fin with end limits on rotation, it is not force controlled within those limits, nor is there centering preload. In addition, the fin is mounted around a narrow central axle, so susceptibility to wear and contamination is high.
Likewise, U.S. Pat. No. 6,439,940 describes a fin and watercraft system in which a pair of fins rotate, and the mechanism by which rotation is achieved is a bearing plate. But, like U.S. Pat. No. 6,053,789, this system lacks a central restoring force, or preload. Consequently, what is needed is a fin system for watercraft that allows a fin to rotate around a fixed axis and makes use of resistive forces applied to the fin so as to provide an assembly or system in which the fin pivots from side to side in a reliable, effective and simple way.